CS 1332 Homework 7: AVL Trees




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You are required to implement an AVL tree. An AVL is a special type of binary search tree that follows
all the same rules: each node has 0-2 children, all data in the left subtree is less than the node’s data,
and all data in the right subtree is greater than the node’s data. The AVL differs from the BST with its
own self-balancing rotations, which you must implement.
All methods in the AVL tree that are not O(1) must be implemented recursively, except for levelorder traversal. Good recursion with simple, focused states is strongly encouraged for this assignment
in particular.
Your AVL tree will implement the AVL interface provided. It will have two constructors: a noargument constructor (which should initialize an empty tree), and a constructor that takes in data to be
added to the tree, and initializes the tree with this data.
Each node has two additional instance variables, height and balanceFactor. The height variable
represents the height of the node (recall that a node’s height is max(child nodes’ heights)+1. The
balance factor of a node is equal to its left child’s height minus its right child’s height. The tree should
rotate appropriately to make sure it’s always balanced.
A note on JUnits
We have provided a very basic set of tests for your code, in AVLStudentTests.java. These tests do
not guarantee the correctness of your code (by any measure), nor does it guarantee you any grade. You
may additionally post your own set of tests for others to use on the Georgia Tech GitHub as a gist. Do
NOT post your tests on the public GitHub. There will be a link to the Georgia Tech GitHub as well as
a list of JUnits other students have posted on the class Piazza.
Homework 7: AVL Trees Due: See T-Square
If you need help on running JUnits, there is a guide, available on T-Square under Resources, to help
you run JUnits on the command line or in IntelliJ.
Style and Formatting
It is important that your code is not only functional but is also written clearly and with good style. We
will be checking your code against a style checker that we are providing. It is located in T-Square, under
Resources, along with instructions on how to use it. We will take off a point for every style error that
occurs. If you feel like what you wrote is in accordance with good style but still sets off the style checker
please email Carey MacDonald (careyjmac@gatech.edu) with the subject header of “CheckStyle XML”.
Javadoc any helper methods you create in a style similar to the existing Javadocs. If a method is
overridden or implemented from a superclass or an interface, you may use @Override instead of writing
When throwing exceptions, you must include a message by passing in a String as a parameter. The message must be useful and tell the user what went wrong. “Error”, “BAD THING HAPPENED”,
and “fail” are not good messages. The name of the exception itself is not a good message.
For example:
throw new PDFReadException(“Did not read PDF, will lose points.”);
throw new IllegalArgumentException(“Cannot insert null data into data structure.”);
If available, use the generic type of the class; do not use the raw type of the class. For example, use new
LinkedList() instead of new LinkedList(). Using the raw type of the class will result in a
Forbidden Statements
You may not use these in your code at any time in CS 1332.
• break may only be used in switch-case statements
• continue
• package
• System.arraycopy()
• clone()
• assert()
• Arrays class
• Array class
• Collections class
Homework 7: AVL Trees Due: See T-Square
• Collection.toArray()
• Reflection APIs
• Inner, nested, or private classes
Debug print statements are fine, but nothing should be printed when we run them. We expect clean
runs – printing to the console when we’re grading will result in a penalty. If you use these, we will take
off points.
The following file(s) have been provided to you. There are several, but you will only edit one of them.
1. AVLInterface.java
This is the interface you will implement in AVL. All instructions for what the methods should do
are in the javadocs. Do not alter this file.
2. AVL.java
This is the class in which you will implement AVLInterface. Feel free to add private helper methods
but do not add any new public methods, inner/nested classes, instance variables, or
static variables.
3. AVLNode.java
This class represents a single node in the AVL tree. Do not alter this file.
4. AVLStudentTests.java
This is the test class that contains a set of tests covering the basic operations on the AVL class.
It is not intended to be exhaustive and does not guarantee any type of grade. Write your own
tests to ensure you cover all edge cases.
You must submit all of the following file(s). Please make sure the filename matches the filename(s)
below, and that only the following file(s) are present. T-Square does not delete files from old uploads;
you must do this manually. Failure to do so may result in a penalty.
After submitting, be sure you receive the confirmation email from T-Square, and then download your
uploaded files to a new folder, copy over the interfaces, recompile, and run. It is your responsibility to
re-test your submission and discover editing oddities, upload issues, etc.
1. AVL.java